Cell surface proteins and glycoproteins are known to participate directly in the processes of cell recognition, adhesion, attachment, and motility (invasion). These processes are involved in the interaction between trophectoderm (blastocyst) and endometrial receptivity to blastocyst adhesion in an estrogen directed, time-restricted process. Current thinking suggests that a restricted number of adhesion-related proteins are part of a larger population of endometrial proteins whose synthesis is stimulated by estrogen. Polyclonal antibodies raised against surface proteins of epithelial or stromal cells separated from the uterus on the day of implantation will be used to detect the small number of adhesion-related proteins. Active antibodies will prevent the in vitro implantation of blastocysts on epithelial or stromal monolayer pretreated with antibody. It is proposed that receptive endometrial cell types, extracted with NP40, will yield adhesion-related proteins that will block action of the polyclonal antibody and permit in vitro implantation. Antiblocking proteins in NP40 extracts will be sequentially isolated, fractionated and purified by conventional methods of protein separation (column chromatography, gel electrophoresis). Separation procedures will be monitored by an electrophoretic immunoblotting method and assayed, against the antibody, in the in vitro implantation system. The restricted number of adhesion proteins related to implantation will be characterized (essentiality of carbohydrate moiety, protein homology) and used as immunogens to develop monospecific antibodies for more detailed studies of the regulatory biochemistry of implantation.